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Implementing Multithread-Safe Singleton in C 11 Without Mutexes
C 11 introduces multithreading features that enable efficient handling of concurrent execution. This article explores a lock-free approach to implementing a lazy initialization singleton in C 11, avoiding the use of heavy-weight mutexes for performance optimization.
Original Approach using Atomic Operations
The presented approach attempts to avoid mutexes by employing atomic operations. However, the proposed implementation relies on CAS (Compare-and-Swap) to prevent race conditions and may be susceptible to subtle concurrency issues.
C 11's Explicit Initialization Guarantees
C 11 introduces strong language guarantees regarding the initialization of static data members. According to §6.7 [stmt.dcl] p4 of the C 11 standard:
If control enters the declaration concurrently while the variable is being initialized, the concurrent execution shall wait for completion of the initialization.
This means that under C 11, lazy initialization of static variables can be achieved without explicit locking, as the compiler will ensure proper initialization synchronization.
Implementing Singleton with Static Member Function
To utilize C 11's initialization guarantees, a simple static member function can be used to access the singleton instance:
<code class="cpp">static Singleton& get() { static Singleton instance; return instance; }</code>
This implementation ensures thread-safe initialization of the singleton instance without the need for explicit locking, making it a viable option in C 11 environments.
Conclusion
While custom lock-free singleton implementations are possible, they can be complex and challenging to get right. In C 11, the built-in initialization guarantees provide a simple and more reliable solution for multithread-safe singleton implementation, obviating the need for complex low-level synchronization.
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